1. Field of the Invention
The present invention relates to a fuel cell hose, and, in particular, to a fuel cell hose for transporting pure water and to a hydrogen hose for transporting hydrogen or hydrogen-containing water.
2. Description of the Art
It is generally understood that fuel cell systems, especially fuel cell systems using polymer electrolytes, will be widely accepted as future power generation systems. However, the portion of a fuel cell system used for generating electricity is vulnerable to contact with foreign matter such as sulfur, metal ions or the like. Therefore, performance of the portion used for generating electricity is drastically deteriorated if such foreign matter enters the portion. For this reason, the hose used in a fuel cell system should have a low extraction property. In other words, it should be difficult for the hose to be extracted by water flowing therethrough and thus the hose should have a high standard of cleanliness. Further, when fuel cell systems especially are used for vehicles, one of the important issues remaining is how to cool the great amount of heat generated thereby. Thus, it is thought that the role taken by the cooling system is significantly important. Further, when the electrical conductivity of a coolant such as LLC (Long Life Coolant) increases in a fuel cell system, electrical short-circuiting tends to occur. Therefore, it is required that the insulation property of internal fluid (water or LLC) be maintained. In other words, a hose used in a fuel cell system is required to suppress ion extraction so as to not increase the electrical conductivity of the fluid.
Heretofore, under such circumstances, a stainless (SUS) tube has been used for the above purposes in fuel cells because of its low ion dissolution. However, when using a SUS tube, it is difficult to mold the SUS tube or to compensate for any installation errors, which causes problems in terms of layout and assembly. In addition, SUS tubes have a problem of poor vibration durability.
For this reason, resin hoses have been recently used for fuel cell hoses instead of conventional SUS tubes. For example, a hose for carrying hydrogen comprising an inner layer made of a material selected from polypropylene (PP) resin, polyethylene (PE) resin, olefin thermoplastic elastomer (TPO), fluorine-containing resin and styrol resin, an intermediate layer made of an ethylene vinylalcohol copolymer (EVOH), and an outer layer made of polyamide resin has been proposed (see, for example, Japanese Unexamined Patent Publication No. 2002-213659).
However, in the case where the inner layer is made of polypropylene (PP) resin, polyethylene (PE) resin or styrol resin for a hydrogen hose as proposed in the above-mentioned publication, the inner layer is hard and inferior in flexibility. Therefore, when such a hose is cooled to a low temperature (about −40° C.) and the hose is bent to 180 degrees, abnormalities such as cracking on an inner or outer surface of the hose may occur, resulting in inferior low-temperature flexibility. Also, defects such as buckling or cracking may occur when a connector is press-fitted to the hose. When the inner layer is formed by the olefin thermoplastic elastomer (TPO), barrier properties against water or hydrogen gas are inferior. When the inner layer is formed by the fluorine-containing resin, a barrier property against hydrogen gas are inferior. Especially, when the inner layer is formed by soft fluorine-containing resin such as tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), a barrier property against water are also inferior.
In view of the foregoing, it is an object of the present invention to provide a fuel cell hose which is superior in flexibility (low-temperature flexing property) and in barrier properties against hydrogen gas or water, and with which no defects such as buckling or cracking occur when press-fitting a connector to the hose.